package com.gadgets.framework.filter;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@Component
public class CorsFilter implements Filter {

    protected final Logger logger = LoggerFactory.getLogger(this.getClass());

    /**
     * The <code>doFilter</code> method of the Filter is called by the container
     * each time a request/response pair is passed through the chain due to a
     * client request for a resource at the end of the chain. The FilterChain
     * passed in to this method allows the Filter to pass on the request and
     * response to the next entity in the chain.
     * <p>
     * A typical implementation of this method would follow the following
     * pattern:- <br>
     * 1. Examine the request<br>
     * 2. Optionally wrap the request object with a custom implementation to
     * filter content or headers for input filtering <br>
     * 3. Optionally wrap the response object with a custom implementation to
     * filter content or headers for output filtering <br>
     * 4. a) <strong>Either</strong> invoke the next entity in the chain using
     * the FilterChain object (<code>chain.doFilter()</code>), <br>
     * 4. b) <strong>or</strong> not pass on the request/response pair to the
     * next entity in the filter chain to block the request processing<br>
     * 5. Directly set headers on the response after invocation of the next
     * entity in the filter chain.
     *
     * @param request  The request to process
     * @param response The response associated with the request
     * @param chain    Provides access to the next filter in the chain for this
     *                 filter to pass the request and response to for further
     *                 processing
     * @throws IOException      if an I/O error occurs during this filter's
     *                          processing of the request
     * @throws ServletException if the processing fails for any other reason
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse resp = (HttpServletResponse) response;
        HttpServletRequest req = (HttpServletRequest) request;
        logger.info("收到【{}】-HTTP请求：{}，请求参数：{}",req.getMethod(), req.getRequestURI(), req.getParameterMap());
        // 不使用*，自动适配跨域域名，避免携带Cookie时失效
        String origin = req.getHeader("Origin");
        if(!(null==origin || "".equals(origin))) {
            resp.setHeader("Access-Control-Allow-Origin", origin);
        }
        // 自适应所有自定义头
        String headers = req.getHeader("Access-Control-Request-Headers");
        if(!(null==headers || "".equals(headers))) {
            resp.setHeader("Access-Control-Allow-Headers", headers);
            resp.setHeader("Access-Control-Expose-Headers", headers);
        }
        // 允许跨域的请求方法类型
        resp.setHeader("Access-Control-Allow-Methods", "*");
        // 预检命令（OPTIONS）缓存时间，单位：秒 缓存10小时
        resp.setHeader("Access-Control-Max-Age", "36000");
        // 明确许可客户端发送Cookie，不允许删除字段即可
        resp.setHeader("Access-Control-Allow-Credentials", "true");
        if("OPTIONS".equals(req.getMethod())){
            // 如果是跨域的OPTIONS请求，就不执行逻辑，直接返回
            resp.setStatus(200);
            logger.info("【OPTIONS】嗅探请求，直接返回应答");
        }else {
            chain.doFilter(req, resp);
        }
    }

    /**
     * Called by the web container to indicate to a filter that it is being
     * placed into service. The servlet container calls the init method exactly
     * once after instantiating the filter. The init method must complete
     * successfully before the filter is asked to do any filtering work.
     * <p>
     * The web container cannot place the filter into service if the init method
     * either:
     * <ul>
     * <li>Throws a ServletException</li>
     * <li>Does not return within a time period defined by the web
     *     container</li>
     * </ul>
     * The default implementation is a NO-OP.
     *
     * @param filterConfig The configuration information associated with the
     *                     filter instance being initialised
     * @throws ServletException if the initialisation fails
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}

    /**
     * Called by the web container to indicate to a filter that it is being
     * taken out of service. This method is only called once all threads within
     * the filter's doFilter method have exited or after a timeout period has
     * passed. After the web container calls this method, it will not call the
     * doFilter method again on this instance of the filter. <br>
     * <br>
     * <p>
     * This method gives the filter an opportunity to clean up any resources
     * that are being held (for example, memory, file handles, threads) and make
     * sure that any persistent state is synchronized with the filter's current
     * state in memory.
     * <p>
     * The default implementation is a NO-OP.
     */
    @Override
    public void destroy() {}

}
